This invention relates to a coupling or connector for disconnecting and shutting off the flow of liquid through the line in which the coupling is placed, and more particularly to a quickly disconnecting connector suitable for use as an emergency breakaway fitting in lines carrying flammable or combustible fluids such as fuel. It is desirable for a breakaway coupling in a fuel line to disconnect at a relatively low tensile force in order to limit damage to the fuel dispensing system, but the force at which a coupling disconnects must also be great enough to withstand axial separation forces on the coupling as a result of fluid pressure. This invention relates to a coupling system that reduces the axial separation forces due to fluid pressure, permitting the use of couplings that separate at a lower externally-generated tensile force.
Fuel, such as gasoline, is commonly dispensed from a fuel pump through a flexible hose and nozzle into the tank of a vehicle such as an automobile or boat. Safety requirements typically provide that controls on the dispenser must be manually activated but must cut off automatically. When the desired amount of fuel has been dispensed, the individual operating the pump removes the nozzle from the fuel tank, turns off the pumping equipment and replaces the nozzle on the dispenser. FIG. 1 illustrates such a system. Occasionally, a vehicle may be driven from the proximity of the dispensing station without first removing the nozzle from the fuel tank inlet. A large number of such occurrences, presently more than 300,000 each year, are reported annually. Instances of this kind are referred to in the trade as a "drive off". Safety regulations require a safety release mechanism with an automatic cut off to terminate flow on such equipment. Without such a mechanism that functions properly, when a drive off occurs, forces generated at the nozzle 34 and transmitted through the hose could dislodge and damage measuring equipment 12 and piping 22 in the pump assembly and could in some cases even dislodge the pump assembly, which is typically anchored to a concrete platform. When such damage occurs, the highly-combustible fuel may be spilled, posing fire and environmental hazards.
Various coupling devices have been developed which are suitable for releasing the nozzle 34 from the pump assembly when the coupling device is subjected to tensile forces above a specified threshold level. The devices, called breakaway couplings or breakaways, are intended to prevent the damage associated with a drive-off. When the nozzle is disconnected, fluid passages in these devices are closed to prevent loss of fuel. Safety regulations in the United States require such a releasing mechanism.
FIG. 2 shows a basic fuel line coupling device with separable body members 44 and 52 held together by a detent 62. These features are common to a number of different breakaway couplings that may vary in the form of detent, body members, valving, or the method of attachment or insertion into the system. For example, the breakaway may offer multiple fluid passages not shown here. The device of FIG. 2 is presented as a representative device to illustrate certain problems common to many different breakaway couplings.
In this class of couplings, tensile force directed along the longitudinal axis 64 of the coupling device (i.e., along the direction of fluid flow) will cause the detent to release the two members of the coupling device, and valves 66 and 72 will then cut off fluid flow through the coupling. The threshhold level at which the detent must release must be sufficiently low to prevent damage to the fuel dispensing system, which typically includes a pump and an underground storage system, not illustrated. Since cabinet anchors may fail at less than 250 pounds and hose connections separate at less than 300 pounds, the breakaway should ideally separate at a lower tensile force.
In the United States, safety rules permit the release mechanism to separate under tensile forces in excess of 200 pounds if the device is properly tested on the specific equipment with which it will be used, while in certain European nations the release mechanism must operate at less than 30 kilograms (approximately 67 pounds) of tensile force.
Some breakaway couplings, like the devices described in U.S. Pat. Nos. 4,667,883, 4,828,183 and 4,827,977, are suitable for mounting between hose segments 24 at some convenient location 40. Other breakaway couplings, such as the devices described in U.S. Pat. No. 4,899,792 and the device shown in FIG. 6 of U.S. Pat. No. 4,667,883 are suitable for use as swivel joint connectors 36. Still other breakaway couplings, such as the devices described in pending U.S. patent applications Ser. Nos. 07/597,886 and 07/597,890 are suitable for mounting directly between the hose and the anchored piping 22. These devices typically rely on some type of detent mechanism for separation.
Looking in more detail at FIG. 2, the first body member 44 is suitable for attachment to the anchored piping system 22 by some convenient means. The first body member 44 includes a fluid passage 46 therethrough from an inlet 48, suitable for being held in fluid communication by some means with the anchored piping 22, to an outlet 50. The first body member 44 is suitable for receiving a corresponding second body member 52, which includes a fluid passage 54 therethrough from an inlet 56, juxtapositioned in fluid communication with the outlet 50 of first body member 44f by some sealing means 58, to an outlet 60 suitable for being held in fluid communication by some means with the nozzle 34. The outlet 50 of first body member 44 is held in fluid communication with the inlet 56 of second body member 52 by a detent 62 which may be either a frangible member such as the shear pin device of U.S. Pat. No. 4,667,883 or a recouplable member such as is shown in U.S. Pat. No. 4,827,977. When a force, either axially directed or axially redirected, in excess of a predetermined threshold, is exerted in direction 64, the detent 62 releases the second body member 52 from the first body member 44 thereby releasing the anchored piping 22 from the nozzle 34 and allowing the inlet 56 of second body member 52 to move from fluid communication with the outlet 50 of first body member 44. As this occurs, valve 66, urged by some means 68, moves into sealing contact with valve seat 70 in first body member 44 to seal the passage from the metering device 12 thereby preventing discharge of pressurized fluid, while valve 72, urged by some means 74, moves into sealing contact with valve seat 76 in second body member 52 to seal the passage from the nozzle 34 and preventing discharge of fluid contained therebetween in excess of the legally mandated maximum loss per separation, which in the United States may be as little as one (1) pint.
While the breakaway coupling is designed to separate under certain conditions, its attachment mechanism should not fail during normal operation when there is no externally-generated tensile force applied to the system. The coupling must therefore withstand axial separation forces that exist in normal operation.
Hydrostatic pressure within the coupled device generates a force between the first body member 44 and second body member 52 at the pressurized interface of the two body members. This force tends to move the second body member 52 axially in direction 78. These hydrostatically produced axial forces therefore act in the same direction as the externally-generated tensile forces, are cumulative, and are restrained solely by the detent 62.
The magnitude of such hydrostatically produced axial forces is relatively large for some breakaways. The hydrostatic forces are the product of the area under pressure and the hydrostatic pressure on that area. The area under pressure within the breakaway is defined and limited by the sealing means 58 which, typically varies from 0.75 inches in diameter to 1.25 inches in diameter. The area under pressure is thus typically in the range of approximately 0.44 square inches to more than 1.56 square inches. In the United States, the maximum normal pumping pressure for fuel dispensing equipment is limited to 50 pounds per square inch guage pressure (Psig.), producing an axial force of between approximately 22 pounds and 78 pounds. This force is small enough that it does not materially affect the ability of equipment to function as planned, but it increases the load on the detent both when it is and when it is not subject to externally-generated tensile force. Thus, one object of the present invention is to reduce the hydrostatically-produced axial separation force on the body members.
Another set of axial separation forces arise in normal operation of a system such as that illustrated in FIG. 1. When the trigger 38 of nozzle 34 is released suddenly, as commonly occurs in fuel dispensing, the column of liquid flowing from a remote location, which may be hundreds of feet distant, and moving at speeds of up to 160 feet per second, is suddenly stopped at the manually operated valve within the nozzle 34. This momentarily pressurizes the confined liquid, producing a pressure wave generally referred to as a Tine shock, which commences at the nozzle and moves through the piping to the remotely located pump. The line shock duration is only milliseconds, but it produces momentary pressures of up to 600 Psig. This momentary 600 Psig. line shock pressure applied to the sealing means produces momentary axial loading on the detent 62 in the range of approximately 220 pounds to 780 pounds of axial force. This is more than the ideal threshold limit of the devices. Since such loading is only momentary, complete failure of the detent does not normally occur after a single line shock but generally does occur after a succession of such shocks.
Accordingly, means are provided for diminishing or removing the axial effect of line shock at pressure-communicating interfaces of breakaway couplings. Several embodiments of the means are given and generally indicated at 100 in FIGS. 3 and 4, 100A in FIG. 5, 100B in FIG. 6, 100C in FIG. 8, 100D in FIG. 11, and 100E in FIG. 12.